Technical Field
The present invention relates to a power conversion device such that it is possible to supply a stable voltage to a load, even when voltage fluctuation in an alternating current power supply or interruption of the alternating current power supply occurs.
Background Art
FIG. 17 is a diagram for illustrating a continuous inverter power supply type of power conversion device disclosed in PTL 1. The power conversion device temporarily converts voltage of an alternating current power supply into direct current voltage, then converts the direct current voltage into alternating current voltage again, and supplies the alternating current voltage to a load.
In the diagram, 1 is a single-phase alternating current power supply, 2 is a capacitor, 3 is a converter circuit, 4 is an inverter circuit, 5 is a filter circuit, and 6 is a load. The capacitor 2 is connected to both ends of the alternating current power supply 1.
An alternating current input terminal of the converter circuit 3 is connected to one end of the alternating current power supply 1. One end of a reactor L is connected to the alternating current input terminal inside the converter circuit 3. The other end of the reactor L is connected to a connection midpoint of a switching element series circuit wherein switching elements Qp and Qn are connected in series. A capacitor series circuit wherein capacitors Cp and Cn are connected in series is connected to both ends of the switching element series circuit. A connection midpoint of the capacitor series circuit is connected to the other end of the alternating current power supply 1. The converter circuit 3 causes the switching elements Qp and Qn to be turned on and off, thereby rectifying the voltage of the alternating current power supply 1, and charging the capacitors Cp and Cn to a predetermined voltage. The capacitors Cp and Cn charged to the predetermined voltage form a direct current power supply.
The inverter circuit 4 is constructed of switching elements Q1 and Q2 connected in series. The inverter circuit 4 is connected to a direct current output terminal of the converter circuit 3. The inverter circuit 4 causes the switching elements Q1 and Q2 to be turned on and off, thereby converting the voltage of the direct current power supply formed of the capacitors Cp and Cn into alternating current voltage.
The filter circuit 5 is configured by a reactor Lf1 and capacitor Cf1 being connected in series. One end of the filter circuit 5 is connected to a connection midpoint of the switching elements Q1 and Q2. Also, the other end of the filter circuit 5 is connected to a connection midpoint of the capacitor series circuit. The filter circuit 5 removes the high frequency contents from the alternating current voltage output by the inverter circuit 4.
One end of the load 6 is connected to a connection point of the reactor Lf1 and capacitor Cf1. Also, the other end of the load 6 is connected to the other end of the alternating current power supply 1. The alternating current voltage output by the inverter circuit 4 is supplied via the filter circuit 5 to the load 6.
FIG. 18 is a diagram for illustrating a continuous commercial power supply type of power conversion device disclosed in PTL 2.
In the diagram, a switch 7 and a secondary coil of a transformer 8 are connected in series between the alternating current power supply 1 and the load. The connection relationships among the converter circuit 3, inverter circuit 4, filter circuit 5, and capacitor 2 are the same as in the embodiment of FIG. 17. Further, an alternating current input terminal of the converter circuit 3 is connected to one end of a primary coil of the transformer 8. Also, a connection midpoint of the capacitor series circuit is connected to the other end of the alternating current power supply 1, and is connected to the other end of the primary coil of the transformer 8. Further, a connection point of the reactor Lf1 and capacitor Cf1 is connected to one end of the load 6.
The power conversion device is such that when the alternating current power supply 1 is sound, the voltage thereof is supplied to the load. Further, when the voltage of the alternating current power supply 1 drops, the converter circuit 3 causes the switching elements Qp and Qn to be turned on and off. In accordance with these operations, compensating voltage for compensating for the drop in the voltage of the alternating current power supply 1 is generated on the primary side of the transformer 8. The compensating voltage is superimposed on the voltage of the alternating current power supply 1 via the transformer 8. Further, voltage that is the compensating voltage superimposed on the voltage of the alternating current power supply 1 is supplied to the load 6. In this case, charging of the capacitor series circuit is carried out by the inverter circuit 4.
Also, when the alternating current power supply 1 is interrupted, the switch 7 is disengaged. Further, the inverter circuit 4 causes the switching elements Q1 and Q2 to be turned on and off, thereby converting the direct current voltage of the capacitor series circuit into alternating current voltage, and supplying the alternating current voltage to the load 6.